There seem to be two basic groups. In the first, the domestic hot water (DHW) is heated by boiler water that runs through a coil in the tank, a sleeve around the tank, or a tank encasing the domestic water tank. Triangle Tube does the last with their SMART tank which has been recommended a few times: http://www.triangletube.com/document...ann_ecs_US.swf



Another is sort of an instant hot water heater running as an indirect water heater. In this case the boiler water sits in the tank and the domestic water flows through the coil. The advantages are that tank doesn't need to be safe for potable water and doesn't have to deal with the mineral deposit of a continuous stream of new water. The disadvantage would appear to be the same as instantaneous hot water systems: does it work?

http://www.ergomax.com/E-Info.htm



Does anyone have experience with the Ergomax? Are their any other similar tanks?

The Ergomax is also available as a boiler storage tank. However, that probably wouldn't work with a mod-con using outdoor reset.

Both Triangle Tube and Ergomax are New Jersey companies.